This invention relates generally to motor speed control and, more particularly, to systems for controlling fan motor speed in a refrigerator.
Refrigeration systems typically use a variety of variable speed direct current (DC) fan motors for air movement and cooling. Fan motors and their associated mounting structures, sometimes referred to as fixtures, have mechanical resonance frequencies that are sometimes approximately equal to the frequency (or multiples and sub-multiples thereof) of the driving frequencies utilized in a pulse width modulation (PWM) based system. As a result, the motor will sometimes be modulated at one or more duty cycles which causes increased perceived noise to a consumer.
Additionally, variations in fan noise can be undesirable and the speed of each fan motor in the refrigeration system is typically controlled to facilitate a reduction in noise variations. PWM is a known method for controlling variable-speed DC fan motors in refrigerators. One known PWM based system utilizes a non-regulated DC power supply with an open-loop control that allows motor speed to vary with the alternating current (AC) line voltage. Another known PWM based system achieves a constant fan speed by using a speed feedback sensor, e.g. a Hall effect device, with a non-regulated DC supply. Other known PWM based systems utilize a regulated DC supply or a voltage regulator circuit to achieve a constant motor speed.
However, utilizing a speed feedback sensor can raise manufacturing costs. Additionally, the constant speed obtained using a regulated DC supply can vary from one motor to another motor due to manufacturing variations among the motors, and voltage regulator circuits are costly and typically have an energy efficiency of less than eighty percent.
In one aspect, a method for controlling speed in a pulse-width-modulation-controlled motor powered by a load voltage source is provided. The method comprises the steps of measuring the motor load voltage, and setting a pulse-width-modulation duty cycle based on the measured voltage.
In another aspect, a method for controlling speed in a pulse-width-modulation-controlled motor powered by a load voltage supplied by a supply voltage is provided. The method comprises the steps of diagnosing motor functionality using a difference between the supply voltage and the load voltage, and switching from motor functionality diagnosis to motor speed control.
In another aspect, a closed loop motor control system is provided. The system comprises a motor, a power source, a resistive element electrically coupling said motor to said power source, at least one switching element electrically coupling said motor to said power source in parallel to said resistive element, and a processor electrically connected to said switching element. The processor is configured to determine a load voltage and set a pulse width modulation duty cycle based on the determined voltage.
In another aspect, a method for operating a motor configured to operate at a variable average speed under pulse-width modulation control is provided. The method comprises the steps of energizing the motor, and setting an average speed by superimposing a sweep frequency onto an average pulse-width modulation frequency.
In another aspect, a motor is provided. The motor comprises a housing, and a stator mounted in said housing, said stator comprising a stator bore. A rotor is rotatably mounted at least partially within said stator bore, and a processor electrically connected to at least one of said stator and said rotor. The processor is configured to determine a load voltage, and set a pulse width modulation duty cycle based on the determined voltage.
In another aspect, a motor comprises a housing, a stator mounted in said housing, said stator comprising a stator bore, and a rotor rotatably mounted at least partially within said stator bore. A processor is electrically connected to at least one of said stator and said rotor, and the processor is configured to set an average speed by superimposing a sweep frequency onto an average pulse-width modulation frequency.
In another aspect, a refrigerator is provided which comprises a housing, a freezer section at least partially within said housing, a fresh food section at least partially within said housing, a motor at least partially within said housing; and a processor electrically connected to said motor, said processor configured to set an average speed by superimposing a sweep frequency onto an average pulse-width modulation frequency.
In another aspect, a refrigerator is provided that comprises a housing, a freezer section at least partially within said housing, a fresh food section at least partially within said housing, a motor at least partially within said housing, and a processor electrically connected to said motor. The processor is configured to determine a load voltage; and set a pulse width modulation duty cycle based on the determined voltage.